The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
As the Claus process is an equilibrium process, presence of hydrogen sulfide in the liquid sulfur in and downstream of a sulfur condenser is inevitable. Unfortunately, dissolved hydrogen sulfide tends to spontaneously degas from the liquid into the headspace of conduits, vessels, pits, and other containers where it ultimately may reach toxic or explosive levels. Moreover, liquid sulfur will also contain appreciable quantities of polysulfides (H2Sx, with x typically between 8 and several hundred), which in turn can decompose into hydrogen sulfide, sulfur dioxide, and sulfur, adding to the hazardous conditions.
Consequently, numerous systems and methods have been developed for the removal of hydrogen sulfide and polysulfides from liquid sulfur. For example, GB2203732B teaches use of a decomposition catalyst in a storage tank that provides for recirculation of the liquid sulfur and uses sweep gas nozzles to expel hydrogen sulfide. A similar process having different treatment zones is described in U.S. Pat. No. 4,729,887A, while U.S. Pat. No. 7,081,233B2 uses static mixers and in-pit treatment of liquid sulfur. Alternatively, as described in US20140377165A1, a process gas is employed to agitate the liquid sulfur in the pit and so expel hydrogen sulfide, while WO2014035614A1 uses sparging mats to expel hydrogen sulfide from the sulfur in a pit. U.S. Pat. No. 4,755,372A uses a degassing zone with a catalyst and further degassing in the sulfur rundown pit with a sweep gas.
Hydrogen sulfide can also be kinetically removed from liquid sulfur as is described, for example, in EP2607304B1 where a relatively fine spray of liquid sulfur is formed in the presence of oxidizing gas in a first compartment, and where the so treated sulfur droplets coalesce into a liquid that is then drained into a second compartment. In a similar manner, U.S. Pat. No. 6,010,677A uses acceleration nozzles that discharge liquid sulfur against an impact target to remove the hydrogen sulfide. Alternatively, U.S. Pat. No. 8,084,013B2 teaches use of a gas-liquid eductor using the liquid sulfur as the ejector motive force and ambient sweep air as the active degassing agent in combination with a static mixer and packed bed.
To render polysulfide and hydrogen sulfide removal more compact, sulfur from a Claus plant can be processed in a single column as described in U.S. Pat. No. 4,844,720A. Here, a decomposition catalyst is disposed in a column that is swept with an oxygen containing purge gas. To further increase reaction rates, high-pressure oxidizing gas may be employed in counter current contact with the liquid sulfur as described in EP851836B1 and U.S. Pat. No. 5,632,967A. On the other hand, where the sweep gas is a low-oxygen or inert gas, sulfur can be degassed using a catalyst on a specific column packing that increases contact of gas bubbles and liquid sulfur as seen in U.S. Pat. No. 8,361,432B2. Similar catalyst structures are also discussed in U.S. Pat. No. 8,663,596B2. Similarly, WO2013006040A1 teaches use of a catalyst module with high void volumes to avoid catalyst attrition, while relatively rapid and efficient mass transfer may also be achieved by use of a stripping gas in the form of small bubbles in the presence of a strong Bronsted-Lowry base as is described in WO9506616A1.
However, despite these various systems and methods, numerous difficulties nevertheless remain. For example, where the catalyst material is used in a vessel with co-current upward flow of sulfur and air for decomposition of polysulfides to hydrogen sulfide and removal of hydrogen sulfide from the sulfur, the catalyst bed frequently becomes fluidized as the sulfur and catalyst densities are very similar, leading to catalyst attrition from abrasion of the particles. On the other hand, where counter-current flow of an oxygen-containing stripping gas is used, water and sulfur dioxide products tend to condense in cooler locations and lead to corrosion. In addition, where the catalyst is immobilized on a packing structure, high pump rates and relatively slow reaction rates are often encountered. Similarly, where desulfuration is performed in the run-down pit, slow reaction times and high circulation rates are often required.
Thus, even though numerous methods of sulfur treatment are known in the art, there still remains a need for improved systems and methods for removal of polysulfides and hydrogen sulfide from liquid sulfur.